The present embodiments relate to medical imaging. In medical imaging, the interior of a patient is scanned. Various approaches are possible, such as magnetic resonance (MR), computed tomography (CT), x-ray, fluoroscopy, ultrasound, positron emission tomography (PET), or single photon emission computed tomography (SPECT). Three-dimensional (3D) visualization is a common practice to assess and record the internal conditions of patients. For 3D visualization, volumetric effects model a wide variety of natural and non-natural phenomena.
3D visualization may be difficult for medical imaging, particularly where the volume data from the scan is rendered with an added surface (e.g., a surface representing a model of an object in the scan volume of the patient). Rendering of surfaces embedded in a volume remains a challenging problem in the traditional volume visualization systems. Several techniques exist (e.g., depth merging and two-way coupling) that implement specific types of global illumination effects near the intersections of the two types of data (e.g. surface transparency, volumetric shadows, or ambient occlusions). The separately handled volume and surface data require complex computations during rendering. For opaque surfaces, existing renderers may use rasterization and apply the resulting depth buffer during volume integration. The resulting rendered volume is then composited over the rasterization result. Multi-pass rendering techniques, such as depth peeling, provide support for embedded transparent surfaces at a significant performance cost. Depth merging of surface data within volume rendering works reasonably well for traditional ray casting, but semi-transparent surfaces need special handling, such as building linked lists per pixel for all surfaces encountered during ray casting through the volume. These techniques partially model the interaction between the volume data and the surface data for a specific visual effect. The techniques fail to capture the full light interaction between the surface and the volume.